1. Field of the Invention
The present invention relates generally to a switch configuration for a keying operation, and more particularly to a key-entry switch device (hereinafter referred to as a key switch) preferably used for a keyboard incorporated as an input device in electronic equipment. The present invention also relates to a keyboard provided with a plurality of key switches.
2. Description of the Related Art
In a thinner or low-profile type keyboard, equipped for a portable electronic apparatus such as a notebook or palm-top personal computer, it is required to reduce the height of a key switch for a keying operation as well as to improve the operability and structural reliability of the key switch. The key switch usable in the low-profile keyboard typically includes a base section, a key top disposed above the base section, a pair of link members interlocked to each other to support and direct the key top in an upward-and-downward direction (or a substantially vertical direction), a switch member including a contact section capable of opening and closing in response to the vertical or upward-and-downward movement of the key top, and a biasing member capable of applying an elastic biasing force (i.e., an initial-position recovering force) in a vertically upward direction to the key top. The key top is movable substantially in the vertical direction relative to the base section, through an interlocking action of the link members, while keeping a predetermined posture of the key top.
Conventionally, in the above key switch, several types of link-member pairs have been used. For example, the first type pair of link members, which may be referred to as a gear-link type, are assembled together into a reverse V-shape as seen from a lateral direction (or in a side view) and meshed at toothed end regions thereof with each other (see, e.g., Japanese Unexamined Patent Publication (Kokai) No. 2003-031067 (JP-A-2003-031067)). The second type pair of link members, which may be referred to as a pantograph type, are assembled together into an X-shape as seen from a lateral direction (or in a side view) and rotatably or slidably joined at intersections thereof with each other (see, e.g., Japanese Unexamined Patent Publication (Kokai) Nos. 2002-231090 (JP-A-2002-231090), 2002-334627 (JP-A-2002-334627), and 2002-251937 (JP-A-2002-251937)). Also, a switch member which is widely used, is configured from a sheet-like switch including a pair of flexible circuit boards respectively carrying contacts in a mutually facing arrangement (referred to as a membrane switch sheet, in this application), the pair of contacts constituting a contact section capable of opening and closing.
The key switch further includes an actuating member making the contact section of the switch member open or close in response to the vertical movement of the key top. For example, the key switch disclosed in JP-A-2003-031067 uses a dome-shaped actuating member made of a rubber, which is disposed between the key top and the membrane switch sheet. When the key top reaches a lower limit position of the vertical movement, the actuating member acts to press, at the inner side of the dome top thereof, the membrane switch sheet, and thus makes the contact section close. On the other hand, the dome-shaped actuating member also acts as the above-described biasing member that is elastically deformed in response to the vertical downward movement of the key top, so as to apply the initial-position recovering force to the key top. In this key switch, during a keying operation of the key top, the actuating member (or the biasing member) is elastically deformed in a buckling manner due to the dome shape thereof, so that the elastic biasing force, non-linearly corresponding to the amount of depression of the key top, is applied to the key top, whereby ensuring unique keying operation properties involving a so-called click feeling.
The first pending technical situation relevant to the conventional key switches is described below. Due to a diversified environment for using a keyboard as an input device of an electronic apparatus, it is required that the keyboard be equipped with a protection structure for protecting an internal structure (e.g., an electrical contact section, a vertically guiding section, etc.) of each of the plurality of key switches installed in the keyboard from the penetration of foreign matter such as dust, liquid and the like. It is known that a separate cover member is provided, as the above-described protection structure, which is additionally or optionally fitted to the keyboard so as to entirely cover the key-arranging surface of the keyboard. However, due to the existence of the cover member, the keying operability for each key switch or the touch feeling of a finger may be deteriorated. Therefore, it is conventionally proposed that a protection function against the penetration of foreign matter is incorporated into the key switch.
For example, Japanese Unexamined Patent Publication (Kokai) No. 10-063394 (JP-A-10-063394) discloses a key switch including a key top slidably guided in a vertical direction relative to a base section, wherein a protection member (or a cup rubber) for preventing dust or liquid from penetrating an electric circuit inside the base section through a gap defined in a slide guide structure of the key top (which includes a tubular guide provided in the base section and a slider provided in the key top) is disposed between the base section and the key top. In this key switch, the cup rubber is a tubular element elastically deformable in response to the vertical downward movement of the key top, and acts to surround the slide guide structure, during vertical movement of the key top, so as to inhibit the penetration of dust or liquid into the base section. The cup rubber also acts, due to the elastic restoring force thereof, as a biasing member for applying an initial-position recovering force in an upward direction to the key top.
The key switch described in JP-A-10-063394 includes the slide-guide type key top frequently used in a keyboard having a normal size, i.e., not a low-profile type. The built-in cup rubber is configured to surround the columnar slide-guide structure formed by the tubular guide of the base section and the slider of the key top, while acting as the biasing member for returning the key top to the initial position. In this configuration, in which the region to be protected against the penetration of foreign matter has relatively narrow gap between the tubular guide and the slider, the protection function required to the cup rubber is not strict, and therefore, the cup rubber can also be used as the biasing member.
However, in the key switch used for a low-profile keyboard, as described in, e.g., JP-A-2003-031067 or JP-A-2002-231090, in which a supporting and directing structure for the key top is formed by a pair of link members interlocked with each other in an openable and closable manner about a mutually joining point, the movable sections of the supporting and directing structure exist in a relatively large area between the base section and the key top, and also a gap permitting an access to the contact section of the switch member (defined at, e.g., an engaging portion between the base section and the link member, an interacting portion between the contact section and the actuating member, etc.) is formed in a relatively large area of the base section. If foreign matter, such as dust, liquid, etc., penetrates the movable sections of the link members or the engaging portions between the base section and the link members, the keying operation properties of the key top may be affected, and, if foreign matter penetrates the interacting portion between the contact section of the switch member and the actuating member, the accuracy of the opening or closing action of the contact may be deteriorated. Therefore, it is required that a key switch used for a low-profile keyboard includes a more strict protection function against the penetration of the foreign matter into the internal structure.
The second pending technical situation relevant to the conventional key switches is described below. In conventional key switches, as described in JP-A-2003-031067 or JP-A-2002-334627, a pair of link members are assembled in an interlockable manner with each other and movably attached to both the base section and the key top. For example, in the key switch disclosed in JP-A-2003-031067, each link member is provided at a first end region thereof with a sliding axle slidably engaged with the base section and at a second end region thereof, opposite to the first end region, with a pivoting axle pivotably joined to the key top and a tooth meshable with a tooth of a counterpart link member in a gearing manner. Correspondingly, the base section is provided with slide support sections having guide grooves for respectively receiving the sliding axles of the link members, and the key top is provided with pivot support sections having bearing holes for respectively receiving the pivoting axles of the link members.
When assembling the key switch of JP-A-2003-031067, the pair of link members are laid on the base section in a flat state (i.e., in a state where the link members do not show the reverse V-shape, but show an opened shape along one plane), with their teeth being meshed with each other, and with their sliding axles being inserted into the respective guide grooves of the slide support sections of the base section. In this state, the key top is pressed onto the link members laid in the flat state, so as to fit the pivoting axles of the link members into the corresponding bearing holes of the pivot support sections of the key top. In order to enable this attachment procedure, the pivot support sections of the key top are provided with notches extending from their outer edges to the bearing holes. When attaching the key top, the pivoting axles of the link members are received in the notches of the pivot support sections and thereby the pivot support sections are elastically expanded, and then, the key top is further pressed on the link members, so as to fit the pivoting axles into the bearing holes in a snap-fit manner.
On the other hand, in the key switch disclosed in JP-A-2002-334627, a pair of link members are mutually joined at their central region in a relatively rotatable manner, and include a first link member that is provided at a first end region thereof with a sliding axle slidably engaged with the base section and at a second end region thereof, opposite to the first end region, with a pivoting axle pivotably joined to the key top, and a second link member that is provided at a first end region thereof with a pivoting axle pivotably joined to the base section and at a second end region thereof, opposite to the first end region, with a sliding axle slidably engaged with the key top. Correspondingly, the base section is provided with a slide support section having a guide groove for receiving the sliding axle of the first link member and a pivot support section having a bearing groove for receiving the pivoting axle of the second link member, while the key top is provided with a pivot support section having a bearing groove for receiving the pivoting axle of the first link member.
Further, the key switch of CP-A-2002-334627 includes an actuator attached to the inner surface of the key top. The actuator includes a pivot support section having a bearing groove for receiving the pivoting axle of the first link member in an auxiliary manner, and a slide support section having a guide groove for receiving the sliding axle of the second link member. According to this configuration, when a force is applied to the key top in a direction detaching the key top from the first and second link members, the force is dispersed so as to reduce damage that may otherwise occur in the respective pivot and slide support sections.
In the key switch of JP-A-2003-031067, in order to improve operability for attaching the key top to the pair of link members, the pivot support sections of the key top are provided respectively with notches extending from the outer edges to the bearing holes. These notches act to allow the pivoting axles of the link members to be easily fitted into the bearing holes in a snap-fit manner, but may allow the key top to be easily detached from the link members.
In particular, when external force is applied to the outer periphery of the key top in a direction pulling-up the key top apart from the base section, the key switch having the link members of the gear-link type shows geometrical properties such that, with regard to a force point (i.e., the outer periphery of the key top), a fulcrum (i.e., one pivot support section farther from the force point) and an application point (i.e., another pivot support section closer to the force point), a ratio of a distance between the fulcrum and the application point to a distance between the force point and the fulcrum is relatively small, and therefore, a force generated at the application point (i.e., a force acting to detach the pivot support section closer to the force point from the pivoting axle of the link member) becomes relatively large. As a result, the pivoting axle may be disengaged from the bearing hole while expanding the notch, and the key top thus may be detached from the link members. Further, a relatively large amount of application force may damage the pivot support section.
In contrast to this, in the key switch of JP-A-2002-334627, due to the provision of the actuator attached to the inner surface of the key top, when force is applied to the key top in a direction detaching the key top from the first and second link members, it is possible to stop damage that may occur in the pivot and slide support sections. However, in the link members of the pantograph type in JP-A-2002-334627, a distance between the support sections (i.e., the pivot support section and the slide support section) on the key top for movably supporting the pair of link members is considerably larger than a distance between the support sections (i.e., the pivot support sections) on the key top for the link members of the gear-link type in JP-A-2003-031067, and therefore, when the external force is applied to the outer periphery of the key top to pull-up the key top apart from the base section as described above, a disengaging force generated at an application point (i.e., the pivot support section or the slide support section) is considerably smaller than a disengaging force that may be assumed in the case of the link members of the gear-link type.
As a result, in the key switch in JP-A-2002-334627, the pivot support section formed in the key top is provided with the bearing groove for directly receiving, in a temporarily retaining manner, the pivoting axle of the first link member, and the pivot support section of the actuator is also provided with the bearing groove for assisting the temporarily retaining function of the direct pivot support section of the key top. In this configuration, if a large disengaging force occurs, which is assumed in the link members of the gear-link type, the key top may be detached from the link member.
The third pending technical situation relevant to the conventional key switches is described below. Due to a diversified environment for using a keyboard as an input device of an electronic apparatus, in the provision of a plurality of key switches in the keyboard, a key switch having a so-called backlight configuration is known, as disclosed in JP-A-2002-251937, in which a marked region defined by, e.g., a character, a symbol, etc., formed in the key top is illuminated from the interior of the key switch, so as to improve the operability of the keyboard in a dark environment. In the key switch of JP-A-2002-251937, a light-emitting section having a LED (light-emitting diode) or EL (electro-luminescence) element is disposed on or below a membrane switch sheet constituting a switch member.
In association with the key switch having the backlight configuration, Japanese Unexamined Patent Publication (Kokai) No. 9-306271 (JP-A-9-306271) discloses a switch for operating a cursor, which has a basic structure different from that of the key switch subject to the keying operation, and which includes a rubber cap for preventing light emitted from the light-emitting section disposed beneath the key top from escaping laterally through a gap between the key top and the base section. The cursor-operating switch of JP-A-9-306271 includes a switch body having a manipulating shaft operable in a pivoting manner into an inclined posture, a key top joined to the manipulating shaft of the switch body, a light-emitting element attached to the switch body, and a cap disposed between the key top and a front plate covering the switch body so as to surround the manipulating shaft. Even when the key top is operated in an inclined manner, the cap closes the gap between the key top and the front plate, thereby preventing light emitted from the light-emitting device from escaping laterally.
In the key switch having the backlight configuration as described in JP-A-2002-251937, it is important to permit the light emitted from the light-emitting section to efficiently reach the marked region of the key top. In this connection, the cursor-operating switch of JP-A-9-306271 includes the cap for preventing the lateral escape of the light emitted from the light-emitting section, but this cap is intended to be installed in the key top of the inclinational type, and it is not considered to apply the cap to the key switch subject to the keying operation.
In particular, in the key switch used for the low-profile keyboard, which includes a pair of link members interlocked with each other in an openable and closable manner so as to act as a support and direct structure for the key top, an opening region formed in the base section is defined in a relatively large area of the base section (e.g., an engaging portion between the base section and the link member, an interacting portion between the contact section and the actuating member, etc.), so that it is necessary to reliably prevent light emitted from the light-emitting section from diffusing through the opening region. Therefore, it is required for the key switch used in the low-profile keyboard to ensure a high-level internal light-shielding function making it possible to more reliably prevent light emitted from the light-emitting section from escaping out from the key switch and permitting the emitted light to efficiently reach the marked region of the key top.